Cast iron pipes are known which are of the type having a stopper ring fixed to the outer periphery of the spigot of the pipe for preventing separation of the pipe from another, the stopper ring being made of steel or tough cast iron (e.g., ductile cast iron). The stopper ring is engageable with a lock ring fitted in a groove formed on the inner periphery of the socket of a mating pipe so that the socket and the spigot are prevented from separating from each other.
Typically, such a known stopper ring is formed as having a circumferentially one-point split configuration and is externally fitted in a groove formed in the outer periphery of the spigot, being then fixed to position by welding. After being so fixed, the stopper ring may be subjected to machining to thereby provide a surface for contact with a socket-side lock ring.
However, this prior art practice involves considerable working complexity, because the outer periphery of the spigot need to be formed with a groove and because welding is required. Furthermore, when machining is effected as above noted, a part of the weld is removed to provide a margin for machining, which may result in strength insufficiency.